The invention relates to a three function heat pump system with a reversible flow refrigerant. More particularly, the invention relates to a three function heat pump system for space heating, cooling and water heating with a receiver which permits refrigerant through-flow in only one direction even though the flow of refrigerant is reversible in the system for heating and cooling.
Three function heat pumps systems are known in which a flow of refrigerant is reversed to obtain heating in winter months, cooling in summer months, and hot water for domestic use. See, for example, U.S. Pat. Nos. 4,693,089; 4,655,051; 4,654,908; and 4,685,307. If a space conditioning tank contains ice, or if the space conditioning tank has a volume which exceeds that of an outdoor heat exchanger, then more refrigerant may be necessary for the heating mode than the cooling mode. Such systems may employ a receiver for surplus refrigerant such that the receiver stores or accumulates excess refrigerant in the cooling mode (summer), and supplies additional refrigerant for the heating mode (winter).
Since the known three function heat pumps reverse the flow of refrigerant, the flow through the receiver is also reversible. This complicates the system since safeguards must be provided to insure proper flow through the receiver and prevent the migration of refrigerant from the receiver to other system components. For example, if the space conditioning tank contains ice, and the system is deactivated, the refrigerant has a tendency to migrate toward the space conditioning tank. Safeguards may be necessary to prevent such migration from the reversible inlets and outlets of the receiver, thereby complicating and increasing the cost of the system.
Accordingly, it is an object of the invention to provide a three function heat pump system which includes a one-way receiver to simplify the system by preventing migration.
It is a further object of the invention to provide a three function heat pump system in which the refrigerant flow in a portion of the system is reversed when switching among the various modes, without reversing flow through the receiver.
It is a further object of the invention to provide a check valve arrangement about the receiver to allow for reversing of the refrigerant flow while utilizing a unidirectional liquid receiver.
It is a further object of the invention to provide a three function heat pump arrangement in which the refrigerant is throttled by a thermal expansion valve when the flow is in one direction, while the expansion valve is by-passed when the flow is in an opposite direction.
These and other objects, advantages and features are provided by the three function heat pump system in accordance with the invention. The system includes a compressor for compressing the refrigerant into a high pressure, high temperature refrigerant. The refrigerant flows within a reversible flow conduit which provides communication among a first heat exchanger or thermal storage tank which provides for space heating; a second heat exchanger for heating domestic hot water; and a third external heat exchanger in the form of an outdoor air-coil.
The system includes a liquid receiver located between the first or second heat exchanger and the third heat exchanger in the heating mode, and between the second heat exchanger and the first heat exchanger in the cooling or hot water production mode. The receiver is surrounded by four check valves which allow for unidirectional flow through the receiver. The location of the receiver and its check-valve arrangement permits the receiver to store excess refrigerant or supply refrigerant to the system as needed in the various modes of operation. The arrangement prevents migration of refrigerant from the receiver to the thermal storage tank. The check valve arrangement also allows for the flow to pass through expansion valves when the refrigerant flows in a first direction, while by-passing the expansion valves when flow is in the second opposite direction.
The system also provides hot water production irrespective of the heating and cooling modes by providing a three-way valve downstream of the hot water heat exchanger to bypass the first heat exchanger. Accordingly, hot water is produced regardless of the heating and cooling modes by directing the refrigerant flow through the external heat exchanger.